X0306 4 2021-12-09 0 0001829802 Sensei Biotherapeutics, Inc. SNSE 0001013023 RICKS THOMAS G C/O SENSEI BIOTHERAPEUTICS, INC. 1405 RESEARCH BLVD., SUITE 125 ROCKVILLE MD 20850 1 0 0 0 Common Stock 2021-12-09 4 P 0 20000 6.62 A 321769 I See footnote Common Stock 2021-12-10 4 P 0 20000 5.86 A 341769 I See footnote The price reported is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $6.515 to $6.75, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set herein. The price reported is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $5.755 to $5.9953, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set herein. These shares are held by the Ricks Family Trust. Thomas Ricks is a trustee of the Ricks Family Trust and accordingly may be deemed to have voting and dispositive power with respect to the shares held by Ricks Family Trust. /s/ Mark Ballantyne (Attorney-in-Fact) 2021-12-13